Watch cover glass and process for the manufacture of such a glass

Abstract

Sapphire watch cover glass or crystal. The glass or crystal (18) comprises on a part of its upper face, a superficial layer (28) having an amorphous structure. This layer (28) makes it possible to increase the hardness of the glass or crystal in its exposed parts while reducing the risk of breakage of said glass or crystal.

What is claimed is: 
     
       1. A sapphire watch cover glass comprising a part adapted to form at least partially the exterior surface of a watch wherein at least said part comprises a zone in which the sapphire presents a superficial layer in which the crystalline structure of the sapphire has been destroyed over a substantial thickness. 
     
     
       2. A sapphire watch cover glass according to claim 1 wherein said part presents ridges wherein said ridges belong to said zone. 
     
     
       3. A sapphire watch cover glass according to claim 1 or claim 2 comprising lateral faces adapted to form a part of the lateral faces of the watch, wherein said zone occupies the lateral faces of the glass. 
     
     
       4. A sapphire watch cover glass according to claim 1 or 2, wherein said thickness is approximately one micrometer. 
     
     
       5. A process for the manufacture of a sapphire watch cover glass according to claim 1 in which the watch glass is cut from a block of sapphire and the faces of the glass are polished, and in which said zone, belonging to one part of the watch and adapted to form at least partially the exterior surface of the watch, is subjected to a treatment to destroy the crystalline structure of the sapphire over a substantial thickness of the sapphire in the superficial layer of said zone. 
     
     
       6. A process according to claim 5 wherein said treatment comprises ionic bombardment of ions having an atomic number between 5 and 45. 
     
     
       7. A process according to claim 6 wherein the ions are selected from the ions of chromium, zirconium, titanium and nitrogen. 
     
     
       8. A process according to claim 7 wherein said ionic bombardment has a density of from 10 16  to 10 18  ions per cm 2  and where the energy of implantation is between 150 and 300 keV. 
     
     
       9. A process according to claim 5, 6, 7 or 8 wherein said thickness is approximately one micrometer.